Preparation of cyclopentadiene



Patented Mar. 23,, 1948 I 2,438,398 PREPARATION OF CYCLOPENTADIENE Robert M. Kennedy, Drexel Hill, Pa., assignor to Sun Oil Company, Philadelphia, Pa., 9. corporation of New Jersey No Drawing. Application August 19, 1947, Serial No. 769,521

3 Claims. 1

This invention relates to dehydrogenation and cyclization of hydrocarbons. Specifically it relates to the dehydrogenation and cyclization of n-pentane, l-pentene, Z-pentene and 1,3 pentadiene to 1,3 cyclopentadiene. More specifically the invention is concerned with a commercially feasible process for the conversion of n-pentane to 1,3 cyclopentadiene by converting the saturated material to 1,3 pentadiene and cyclizing the 1,3 pentadiene to 1,3 cyclopentadiene.

The conversion ofpentane to 1,3 cyclopentadiene is considered to take place by way of, say, l-pentene and 1,3 pentadiene. The yield of 1,3 cyclopentadiene will be higher when the char ing stock requires the least amount of dehydrogenation. Accordingly, the invention will be described with reference to the conversion of 1,3 pentadiene to 1,3 cyclopentadiene to which it is pre-eminently suited. The reactions of the fore= going enumerated steps can be represented as follows:

(l-pentene) H J--H (1,3 pentadlene) CH ll (1,3 cyclopentadiene) CH and elficient heating of the charge stock can be employed. Suitable contact masses which can. be employed are described and claimed in the following copending applications for patent filed by the present inventor together with Stanford J. Hetzel: Serial No. 630,691, filed November 24, 1945, now Patent 2,438,399; Serial No. 030,092, filed November 24, 19%, now Patent 2,438,400; Serial No. 636,270, filed December 20, 19%, and Serial No. 650,394, filed February 26, 19%, now Patent 2,438,401 and are "silica gel, "chromia on alumina, activated alumina. and silicon carbide," respectively.

The temperature employed for the dehydro genation of the hydrocarbons, in the instant case 1,3 pentadiene, will vary depending upon the other conditions of operation, on the nature or purity oi the charging stool; and on the contact mass, it any, employed. The conversion of l,3 pentadiene can be advantageously enacted at a temperature within the range 300 C. to a tempelature beyond which excessive decomposition of the hydrocarbons will take place. More spe cihcally a temperature within the range s00 G.- 700 6., preferably 450 C.-650 0., can be em ployed.

While the conversion per pass is substantially independent oi pressure it has been found that lower pressures seem to form higher yields on recycling. Accordingly, while higher and lower pressures are not excluded from the scope at the invention, pressures in the range of 1000 mm. rig-10 mm. Hg absolute, pregerably 200 mm. big-- 10 mm. Hg, can be employed.

The time during which the 1,3 pentadiene is subjected to a' dehydrogenating temperature is a factor to be considered. There appears to be an optimum range of time, that is, 0.06 second to 00 seconds. When a contact mass has been em ployed the optimum range of contact time has been found to correspond to charging rates of I 0.25 gram/minute/ grams-10 grams/min ute/100 grams of contact mass. However, higher and lower charging rates are not excluded from the scope of the invention.

tion:

Example 1 1,3 pentadiene of approximately 88% pentadiene content was fed to a reaction tube consisting of a length of ordinary carbon steel pipe approximately one inch inside diameter and havin a volume of, 128 cc. The pipewas maintained at 600 C. by external heatingmeans and the sys- The following examples illustrate the inven- 3 tem was evacuated in a controlled manner such that while the liquid pentadiene was being fed into it, the pressure remained at 30 mm. Hg absolute pressure. Means were provided {or vaporizing the 1,3 pentadiene before it entered the reaction tube and preheating it to approximately 550 C. The rate of feed was maintained constant Example 2 With the same apparatus and technique as in Example 1, the same charge of 1,3 pentadiene was cyclized at 615 C., 15 mm. Hg and a residence time of 0.78 second. A once-through yield of 3.8% cyclopentadiene was obtained with a calculated ultimate yield of 30.4%

It will be apparent to those versed in the art that modification and variation are possible within the scope of the invention as defined in the appended claims, the essence of the invention being that n-pentane, l-pentene, Z-pentene and/or 1,3 pentadiene can be de ydrogenated and cycllzed to 1,3 cyclopentadiene by subjecting these compounds to a dehydrogenation temperature. That 4 any five carbon straight chain hydrocarbon could be cyclized by subjecting it to a dehydrogenation temperature was not predictable.

I claim:

1 1. A process for the dehydrogenation and cyclization of 1,3 pentadiene to 1,3 cyclopentadiene which comprises subjecting said 1,3 pentadiene to dehydrogenation at a temperatur within the range of 300 C. to 700 C. for a time suilicient to eflect a desired extent of dehydrogenation and cyclization.

2. A process for the dehydrogenation and cyclization of 1,3 pentadiene to 1,3 cyclopentadiene which comprises subjecting said 1,3 pentadiene to dehydrogenation at a temperature within the range of 400 C.-700 C. for a time sufllcient to effect a desired extent of dehydrogenation and cyclization.

3. A process according to claim 2 wherein the pressure is within the range of 1000 mm. Hg to 10 mm. Hg.

ROBERT M. KENNEDY.

REFERENCES CITED UNITED STATES PATENTS Name Date Frey June 18, 1946 Number 

